The object of any laboratory test is to simulate some physical phenomenon as closely as possible, making sure that all of the physical independent variables are represented and controlled. Also the dependent variables must be measurable in a statistically meaningful manner. In the case of fouling tests, the independent variables of interest are fluid pressure, fluid temperature, surface temperature, fluid velocity, and fluid composition. The dependent variable is the actual mass or volume of deposit which accumulates on a particular surface in a given time. The dependent variable is referred to as the deposition rate. Another object of a laboratory fouling test is to determine an effect of an independent variable on the deposition rate. For example, the fluid composition may be changed by adding a variety of chemicals which may in turn affect the fouling rate.
One such as the inventor hereof, having spent many years in the field of fouling research and conducted many fouling tests, will have experienced frustration with the fouling tests because the fouling rate is difficult to control and is not very reproducible even when all other independent variables are controlled and/or held constant. Many of those experienced in this particular field claim to have fouling tests which have reproducibilities better than 10%. However, it has generally been conceded by those experienced in this art that fouling tests usually reproduce the fouling rate by no more than 50%. In many cases this makes the test useless in determining the effect of some independent variable, such as fluid composition, because the fouling rate changes more by itself than by changing the independent variable. Therefore, many tests must be conducted at the same conditions in order to produce statistically meaningful results. This can be costly and time consuming because each fouling test requires between 3 and 24 hours to complete.
The primary cause of the fouling of surfaces used to heat processed fluids is that dissolved or suspended contaminants which occur in the fluids are degraded when exposed at elevated surface temperatures, forming solids or semisolids in the form of polymers, coke, salts, and other inorganics. Therefore, it is critical that surface temperature be well known and controlled. The difficulties with controlling surface temperature is that there are so many other variables, than fouling deposits, which have a major influence. Some of the other variables are, fluid velocity, fluid composition, fluid temperature and system pressure. Only when all of these variables are controlled can meaningful laboratory fouling test data be gathered.
In designing apparatus and procedures of the type involved, the problem is to generate and measure in a laboratory environment a fouling deposit representative of that produced in the field. The information obtained by carrying out such fouling tests enables many anti-foulant treatments to be evaluate as well as other factors which may mediate the fouling process.
My prior U.S. Pat. No. 4,383,438 describes fouling test equipment which is an example of fouling test apparatus for conducting single fouling tests for each cycle of operation, thereby requiring significant expenditures for conducting multiple tests. It is desirable therefore to provide fouling test apparatus having the capability of simultaneously conducting multiple tests to thus provide a wide range of useful commercially efficient test information within a reasonably short period of time.
During the conduct of fouling tests a quantity of the foulant leaves solution and becomes deposited on a heated foulant receptacle surface. The concentration of the foulant in the test solution is thus depleted by the quantity deposited and the rate of fouling can change. Subsequent fouling tests using this test fluid or another quantity of fluid from the same batch may not have satisfactory reproducibility. It is desirable therefore to provide a fouling test system wherein multiple fouling tests may be conducted through employment of a single test fluid sample and the results of the tests will exhibit optimum reproducibility.
It is a principal object of this invention to produce fouling tests for evaluating the effect of physical parameters which affect the fouling rate.
It is another feature of this invention to provide novel equipment that is capable of reducing the time and costs required to generate statistically meaningful fouling test data.
It is a further feature of this invention to provide means for simultaneously conducting a plurality of fouling tests during each test procedure.
It is also another feature of this invention to provide means for insuring that independent variables such as fluid velocity, fluid temperature, surface temperature and fluid composition are well known and controlled.
It is an even further feature of this invention to insure that the laboratory fouling data of this invention is comparable to data collected from actual plant environments.
It is another feature of this invention to provide means for efficiently calibrating the fouling probes of the apparatus so that surface temperature is well known.